Field of the Invention
The present invention relates to a capacitance type transducer to be used as an ultrasound transducer or the like, and a method of manufacturing the capacitance type transducer.
Description of the Related Art
Hitherto, micromechanical members to be manufactured using micromachining technology may be processed on the order of micrometers, and various functional microelements are realized using such micromechanical members. A capacitance type transducer using such technology is being researched as an alternative to a piezoelectric element. With such a capacitance type transducer, an acoustic wave such as an ultrasound wave (hereinafter sometimes represented by ultrasound wave) may be transmitted and received using vibrations of a vibrating film, and in particular, excellent broadband characteristics in a liquid may be obtained with ease. It is to be noted that the term “acoustic wave” as employed herein encompasses waves called a sonic wave, an ultrasound wave, and a photoacoustic wave. For example, the term “acoustic wave” encompasses a photoacoustic wave generated in an object when the inside of the object is irradiated with light (electromagnetic wave) such as visible light or infrared light.
Regarding the above-mentioned technology, there has been proposed a capacitance type transducer in which a parasitic capacitance is reduced by extracting wiring from an upper electrode embedded in a membrane on an upper side of the membrane (see Japanese Patent Application Laid-Open No. 2011-234061). Further, there has been proposed a capacitance type transducer in which through wiring is provided in a membrane so as to reduce fatigue caused by a stress of an upper electrode embedded in the membrane (see Japanese Patent Application Laid-Open No. 2008-283618).
In the case of manufacturing a broadband capacitance type transducer with a high-output acoustic pressure, a high-efficiency capacitance type transducer can be obtained by setting a distance between electrodes to be small. However, with such a configuration, there arises a problem of a reduction in withstand voltage, which limits a voltage to be applied, with the result that it is not easy to produce a large acoustic pressure. On the other hand, a broadband can be achieved if the mass of a vibrating film is lowered by using a thin membrane as the vibrating film. However, according to a related-art manufacturing method involving sealing a gap after forming an upper electrode, the thickness of the vibrating film fluctuates and the fluctuations in gap are caused by warping, with the result that it is not easy to manufacture a high-performance device. Further, according to a method involving forming a hole in a sealing film to conduct electricity with though wiring, it is not easy to form a thin film although the withstand voltage is ensured, and a band is likely to be narrow.